Similar to the widely use of translucent agro-film based on polythene, polyvinyl chloride, and polypropylene, the use of photo-transforming agro-film is currently getting popularity, creating a much stable micro-weather in hot bed and green house. It can help protect seedlings and crops in the first spring frost and can significantly increase temperature in the growth period during summer. As a result, the application of photo-transforming agro-film has been reaching far and wide.
The phosphor filled in the agro-film can transform the short-wave portion of light, mainly the ultraviolet of the solar radiation (about 6% of the light in the middle latitude region) into the red and dark red light of the photosynthesis spectrum in visible spectrum. The red spectrum was first discovered by K. A. Timiriazev, Russian scientist. It is the essential ingredient for photosynthesis and carbohydrate (containing mainly glucose, C6H12O6), which involves carbon dioxide and its formula of the chemical reaction can be expressed as:6CO2+6H2O→C6H12O6+6O2↑ °
Blue spectrum is less active in photosynthesis and yet is necessary in forming the nutritional tissues of green plant's roots and leaves. On the other hand, as established by K. A. Timiriazev and other biologists, the green-orange spectra affect only some plants' photosynthesis. They can substitute the major green pigment, a- or β-chlorophyl, predominately β-based pigment (refer to Photo-transforming Agro-film, International Nanotechnology Conference Proceeding, Nanotechnology Industry, Moscow, pp. 124-140, 2006,authored by one of the present inventors, N. P. Soshin).
Intensive use of agro-film can render green plants in a closed soil chamber to undergo stable photosynthesis. The agro-film has been protected by Russian Patent 2160289 (refer to Russian 2160289 awarded to one of the present inventors, N. P. Soshin), which discloses a polythene film commercially branded as “HARVEST.” The film is filled therein with phosphor based on Y2O2S:Eu phosphor powder. The film is 100-150 μm thick and has a number of advantages in a closed soil chamber: 1. The ripe period of the first harvest is 1.5-2 weeks shorter; 2. the yield for vegetable, fruit, and economic crop has been substantially enhanced by 25-75%; 3. the temperature of the spring growth period is increased by 5-8° C.; and 4. sun burn of plants can be prevented.
Meanwhile, apart from proved and expected results, the photobiological reaction resulted from conventional agro-films has other unexpected advantages, including the enhancement of vitamin C and other trace elements in berry, vegetable, and fruit by one to two times. The advantage is usually associated with the narrow radiation frequency band of the inorganic phosphor based on Y2O2S:Eu, which has a wavelength of λ=626 nm. The luminance intensity of the radiation spectrum of the phosphor in the subband described above is equal to or higher than that of the narrow spectrum of the solar radiation. The aforementioned advantages of the phosphor based on Y2O2S:Eu have been widely confirmed in different climatic zones of the Earth. This has been disclosed in a Canada Patent, CA 2348943, awarded to Bolchoukhine, and in a Mexican patent, MX 1004165, awarded to one of the present inventors, Soshin. These two patents are therefore taken as a reference for the present patent.
Although the aforementioned sulfur oxide phosphor has the advantages described, there are substantive drawbacks, including the mass characteristic of the Y2O2S:Eu phosphor and the wide distribution of particle size of polythene.
Main drawbacks are described as follows: 1. The concentration of ultrafine particle is not high, less than 103 particles/cm2 (agro-film area), leading to the low luminance intensity of the agro-film; 2. The cost is too high with 1 m2 of agro-film requiring 150 g of polymer material: and 3. The substantive drawback of the agro-film, according to the inventors' opinion, is related to by the over-sized particles of phosphor used for the filler of agro-film, the mean particle size being dcp=10-12 μm and the largest size being d≈30-35 μm.
Material synthesis technology experiments have been conducted to resolve the drawbacks associated with the phosphor based on Y2O2S:Eu. One of the present inventors, N. P. Soschin, has been awarded a Russian patent, SU 1450358, which discloses the batching method for materials and semi-products required. The materials disclosed in the patent have been selected as a prototype for further improvement; the luminance intensity can be enhanced by 10-15%, but the increase in the volume concentration per unit area of phosphor is not significant.
Accordingly, the present invention is aimed to improve the aforementioned drawbacks of the conventional technology, namely low volumetric concentration and relative luminance intensity of the sulfur oxide phosphor used in agro-film.